Q:

How do volcanoes form?

A:

Quick Answer

Commonly, volcanoes form at points where the Earth's crust is thinnest. This is normally near fault lines, but has been known to occur in the middle of tectonic plates or even in subduction zones, where one plate is pushing another plate down under it.

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Full Answer

Volcanoes begin as vents on the ocean floor or geothermal hot spots on the Earth's surface. Hawaii's volcanic activity is one example of molten rock finding its way to the surface through vents in the ocean floor. Meanwhile, Mount St. Helens is an example of a subduction zone volcano. In both instances, magma has pushed its way up from the mantle and into the upper crust. With vent formations, lava builds up over time, layering on top of itself, and eventually a mountainous formation develops. With subduction zone volcanoes, the mountain forms first, with molten rock pushing up through thin layers of crust. This was part of why the eruption of Mount St. Helens was so dangerous, as the pressure of the heated magma built up over time and caused the top portion of the mountain to be blasted away. Of course, every volcanic eruption is dangerous, though the characteristic lava eruptions make much slower progress than the energetic activity found in previously dormant volcanoes.

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Related Questions

  • Q:

    How do volcanoes occur?

    A:

    Volcanoes occur when molten rock from underneath the Earth's crust rises up. This molten rock comes from the mantle, not from the Earth's core. Because of plate tectonics, volcanoes can form relatively quickly.

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  • Q:

    Why do volcanoes happen?

    A:

    A volcano occurs when molten rock wells up from the mantle to breach the Earth's crust. Most commonly, this occurs around the edges of tectonic plates. When two plates collide, one may slide underneath its neighbor, opening a channel for magma to reach the surface. If two plates pull away from each other, the resulting gap may allow multiple channels for magma to escape.

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    When do volcanoes occur?

    A:

    Volcanoes occur when magma is able to reach the surface of the Earth through a gap in the crust. This typically occurs at plate boundaries, where two tectonic plates pull away or move against each other. Volcanoes can also form at weak points in plates, called hot spots.

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  • Q:

    Where do volcanoes come from?

    A:

    Volcanoes are formed when the molten rocks and gases under the earth break through the crust and erupt. A volcano can be a crack, a dome or a mountain with a crater at the top.

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